Devices which combine image display capabilities with image capture capabilities are well known with the most well known form being the combination of the laptop computer with the webcam. This combination enables the simultaneous display of images with the capture of images of the scene in front of a laptop computer. As communication bandwidth increases the use of visual communication techniques, such as video communication becomes increasingly popular. However, there remains a need for an integrated device that integrates the image capture capabilities into the display, both to simplify the operation for the user and to enable an improved capture of the scene that the displayed image is being shown to. This is particularly important when considering video communication where it is desirable to capture an image of the viewer such that their eye gaze appears to be looking directly at another viewer when their image is displayed on the other viewer's display. This need for an integrated device extends across all displays from large wall displays to small hand held displays such as cell phones.
Liquid crystal displays (LCD) are well known in the art. LCDs with backlight assemblies that include a light guide or a distributed illumination panel constitute a uniform light panel with a thin format and as such are desirable for many display applications where space is limited, including but not limited to: cell phone displays, computer monitors, laptops, televisions and automobile displays. The invention discloses a modified LCD with a backlight assembly that includes a light guide or a distributed illumination panel in a uniform light panel that comprises a thin display with an integrated image capture device. The thin display with integrated capture can be used for visual exchanges or video communication with another user. The thin display with integrated capture can also be used as a digital mirror device. In addition, the thin display with integrated capture can be used to collect information about the scene in front of the display to optimize the display parameters or to tailor the content displayed.
Thin displays are generally desirable for most display applications. LCD type displays tend to be much thinner than cathode ray tube (CRT) displays, as such they are more desirable for large screen displays since they take up less room in the home or office. Typical thicknesses are 50 mm in depth for an LCD television as compared to 400 mm in depth or more for a CRT television. The thinner form factor of LCD type displays makes them much more suited to portable devices where thin form factors are very important, and the thickness of cell phone and laptop displays can drop below 5 mm. In fact Samsung Electronics Co. (Seoul, Korea) has announced a new type of LCD display called i-Lens that has a reported display panel thickness of 0.82 mm. In such applications, it is desirable that the addition of an integrated image capture device should not increase the thickness of the display device substantially.
In U.S. Pat. No. 5,340,978 entitled “Image Sensing Display Panels with LCD Display Panel and Photosensitive Element array”, Rostoker et al describe an image sensor with distributed image capture that can be used in an image sensing display panel. However, in the embodiments disclosed by Rostoker, the photosensitive elements will interfere with the backlight operation causing low overall brightness or shadowing in the displayed image or shadowing in the captured image. In Col. 15, Line 18-23, Rostoker states that “backlighting will generally interfere with the operation of the photosensitive array. As a result, it will be necessary to “turn off” the backlighting means while the video signal from the photosensitive array is being monitored.” Backlights with fluorescent light sources cannot be turned off quickly and any time that the backlight is turned off will decrease the perceived brightness of the displayed image.
In United States Patent Application US 2004/0257473, entitled “Display device having an image pickup function and a two-way communication system”, Miyagawa describes a display device having light emitting pixels with transmittancy and an image capture device which captures an image through the display. Miyagawa discloses light emitting pixels and as such does not address an LCD with a backlight assembly wherein the light is provided by a backlight that includes a light guide. The light emitting pixels as disclosed by Miyagawa, either are transparent and emit light equally toward the display side and the capture side, thereby reducing efficiency or the light emitting pixels are opaque and emit only on the display side thereby interfering with the incoming light for the image capture. In addition, Miyagawa addresses stray light in the captured image by correcting the image after it has been captured using a correction circuit (paragraph 0117) and does not attempt to reduce the stray light which contributes to a reduction in contrast in the image due to flare and a loss in dynamic range of the image. Further, the angled mirror device described by Miyagawa increases the thickness of the image capture and display device substantially. In one embodiment, Miyagawa describes using an LCD panel with an aperture in the polarization plate to allow the image capture device to see through the panel, however the aperture creates an area in the display where an image cannot be displayed.
In United States Patent Application US 2005/0024489 entitled “Image Capture and Display Device”, Fredlund et al disclose a display device for capturing and displaying images along a single optical axis. In the device described by Fredlund, the backlight includes an angled mirror and a light which is reflected off the mirror from a remote location as well as a remote location for the image capture device. In addition, Fredlund discloses a flickering light to reduce stray light during image capture similar to Rostoker. The solution described by Fredlund is not well suited to making a thin or compact display and capture device.
In U.S. Pat. No. 5,159,445 entitled “Teleconferencing Video Display System for Improving Eye Contact”, Gitlin describes a LCD display with a backlight assembly that has a hole for a camera. However, the backlight assembly described by Gitlin includes a reflector without a light guide that is not well suited to providing a uniform illumination to the display.
Uniform illumination is important to the perceived image quality of the display. In “Digital Imaging Colorimeter for Fast Measurement of Chromaticity Coordinate and Luminance Uniformity of Displays” by D. R. Jenkins, D. C. Beuzekom, G Kollman, C. B Wooley, R. Rykowski; SPIE Proceedings of Flat Panel Display Technology and Display Metrology II Volume 4295, April 2001, pp 176-187, uniformity of illumination in displays and the measurement of uniformity is discussed with 23-25% non-uniformity presented as typical for an LCD when measured at 9 points across the display. In “Assessment of Display Performance for Medical Imaging Systems: Executive Summary of AAPM TG18 Report” by E. Samei et al., Medical Physics, Vol. 32, No 4, April 2005, pp 1205-1225, it is recommended on pp 1206 that for medical displays, the non-uniformity should be less than 30%. Consequently, uniform illumination is important for the display. It is desirable that when adding an integrated image capture device that it should not noticeably degrade the uniformity of the display.
While image capture and display devices have been described in the prior art, there remains a need to provide an image capture and display device, which is thin and provides a substantially uniform displayed image. To enable high quality imaging on the display, means are required to reduce the non-uniformity in backlight illumination due to the presence of the image capture device. The display must also allow for high quality images to be captured while the image capture device remains unobservable. In addition, techniques to reduce stray light from impinging on the image capture device and thereby reducing captured image quality are needed.